Magnetic nanoparticles modified by citrate groups for magnetically responsive photonic crystals

Induced by appropriate magnetic field, Fe 3 O 4 nanoparticles self-assemble into magnetically responsive photonic crystals (MRPC), showing the potential applications in color display, bioimaging agents and sensors. We report a kind of Fe 3 O 4 clusters synthesized by one-pot hydrothermal reaction with the attachment of a small molecule (citrate groups) on the surface, which increases negative charge density and demonstrates the characteristics of good water-dispersity and stability. The characteristics of the nanoparticles are measured by TEM , SEM, FT-IR, XRD , XPS , TG and VSM. The variation of Fe 3 O 4 nanoparticles size is determined by the amount of citrate. The MRPC show tunable photonic performance under a magnetic field ranging from 80 to 374 G, which could be controlled by the size, concentration, washing method and washing cycles.